Free trade agreement between North American countries lets products made in North America cross NA borders with no duty.

Not all of them, there are some exceptions. But I got lucky and the diapers apparently fall in that category, even though the Tots Bots are not made in North America. In fact the invoice did not state where the diapers where made and the package seemed intact, so I don't know how they would know at the border where the diapers where made.